The present invention relates generally to a system for regulating the high pressure component of an economized refrigeration system by regulating the amount of refrigerant in the high pressure component of the system with an interstage accumulator positioned between an economizer heat exchanger and a compressor.
Chlorine containing refrigerants have been phased out in most of the world due to their ozone destroying potential. Hydrofluoro carbons (HFCs) have been used as replacement refrigerants, but these refrigerants still have high global warming potential. “Natural” refrigerants, such as carbon dioxide and propane, have been proposed as replacement fluids. Unfortunately, there are problems with the use of many of these fluids as well. Carbon dioxide has a low critical point, which causes most air conditioning systems utilizing carbon dioxide to run partially above the critical point, or to run transcritical, under most conditions. The pressure of any subcritical fluid is a function of temperature under saturated conditions (when both liquid and vapor are present). However, when the temperature of the fluid is higher than the critical temperature (supercritical), the pressure becomes a function of the density of the fluid.
When a refrigeration system is run transcritical, it is advantageous to regulate the high pressure component of the system. By regulating the high pressure of the system, the capacity and/or efficiency of the system can be controlled and optimized.
In the prior art, the high pressure component of a refrigeration system has been regulated by adjusting an expansion valve located at the exit of the gas cooler, allowing for control of system capacity and efficiency. Suction line heat exchangers and storage tanks have also been employed to increase system capacity and efficiency.
System capacity can also be increased by employing an economizer heat exchanger to subcool the liquid refrigerant exiting the heat rejecting heat exchanger. The refrigerant is split into two flow paths after leaving the heat rejecting heat exchanger. An economizer flow path is expanded to a low pressure and exchanges heat with a main flow path in the economizer heat exchanger. The refrigerant from the economizer flow path is injected into the compressor. The refrigerant in the main flow path is expanded by the main expansion device. By further cooling the main flow path with the refrigerant in the economizer flow path, the inlet enthalpy to the evaporator decreases, increasing cooling capacity.